A dual-function electrical hand drill provides not only a rotation output but also a to-and-fro vibration output. A mode switch is provided on such a dual-function hand drill to switch between rotation output mode and vibration output mode. Such a dual-function electrical hand drill is available in the market and an exemplary structure thereof is illustrated in FIGS. 7 and 8 of the accompanying drawings. As illustrated, the dual-function electrical hand drill, designated with the reference numeral 900, generally has a pistol shape. A handle 910 having a power switch 911 is provided to be held by hand of an operator. A casing 912 extends forward from the top of the handle 910 to house therein a torque source or a rotation source, such as an electrical motor 913 (see FIG. 8). The motor 913 is controlled by the power switch 911.
A chuck 914, which is not shown in FIG. 8, is mounted on the front end of the casing 912 to be rotatable with a spindle 932 (FIG. 8) of the motor 913 by the coupling of a driving shaft 930. The dual-function electrical hand drill 900 further comprises a torque setting ring 915 which allows a user to set to the desired output torque. In the example illustrated, the output torque levels are respectively indicated by 1-5 and a "bit" mark which represents the maximum output level. An indicating mark 916 is provided on the casing 912 to show the selection of the output level.
The dual-function electrical hand drill 900 further comprises a mode switch ring 917, on which two marks 918 and 919 are provided to respectively represent the rotation mode and the vibration mode. The two output modes are selected by rotating the mode switch ring 917 to have one of the marks 918 and 919 registered with a marker 920 formed on the casing 912.
To operate the dual-function electrical hand drill 900 in the vibration mode, the output torque level must be set to the maximum output, the "bit" sign, and then the mode switch ring 917 is rotated to select the oscillation mode. This is a two-step operation.
FIG. 8 is a cross-sectional view of the conventional dual-function electrical hand drill 900 with the casing 912 and the chuck 914 removed. The dual-function electrical hand drill 900 comprises a speed reduction gear train 940, basically constituted by three planetary gear sees, enclosed by a stationary enclosure member 42 which is fixed to the motor 913. The speed reduction gear train 940 is coupled between the driving shaft 930 and the spindle 932 of the motor 913 so as to transmit the rotation of the spindle 932 to the driving shaft 930.
Torque setting means 950, which is controlled by the torque setting ring 915, is provided to control the output speed of the last stage planetary gear set so as to change the output speed and thus the output torque of the driving shaft 930.
Mode selection means 960, which is controlled by the mode switch ring 917, is provided on the front end of the dual-function electrical hand drill 900. The mode selection means 960 comprises a serrated-member pair which, if allowed to engage each other, moves the driving shaft 930 to and fro during rotation, so as to provide the vibration output. Means for disengaging the serrated-member pair is provided to allow the driving shaft 930 to be rotated without the to-and-fro movement.
Although the conventional dual-function electrical hand drill shown in FIGS. 7 and 8 works well, there are several disadvantages existing in the structure of the known dual-function electrical hand drill. These disadvantages include:
(1) It requires complicated operation to switch from the rotation output mode to the vibration output mode, for it needs a two-step operation, namely the torque setting step (to maximum torque) and the mode switch step.
(2) It requires the torque setting ring to be set to the maximum output level before the vibration mode is selected and since the two settings are conducted independently by turning two different setting members, it may cause an operation fault in switching to the vibration mode without setting to the maximum torque output in advance.
(3) Due to the use of two setting rings, the overall length of the electrical hand drill has to be increased and this causes a worse operation controllability for it may generate a greater reaction torque to the hands holding the drill.
It is therefore desirable to provide a dual-function electrical hand drill which is needs only one setting member so as to overcome the above-mentioned problems associated with the conventional dual-function electrical hand drill.